THURSDAY, May 1, 2003 (HealthDayNews) -- For the first time, scientists have managed to "grow" mouse eggs from mouse embryonic stem cells in a laboratory setting -- and these eggs divided and developed into embryos.
The feat, reported in the May 2 issue of Science, proves that embryonic stem cells can develop into any and every type of cell outside the body, not just tissue cells.
This landmark event comes almost a quarter century after another historic occasion: the birth of Louise Brown, the world's first test-tube baby, who turns 25 on July 25.
"It's an important paper," says Paul Sanberg, a professor of neurosurgery at the University of South Florida in Tampa and director of the school's Center for Aging and Brain Repair. "It's basically more proof that mouse cells or embryonic cells can be totipotent, or can become anything."
While many scientists spend years trying to replicate laboratory findings in human beings, these researchers were trying to do the opposite. No one had been able to accomplish this up to now because "there was no good marker to follow the process, to see what was happening," explains study author Hans Schöler, a professor of reproduction medicine at the University of Pennsylvania School of Veterinary Medicine and director of Penn's Center for Animal Transgenesis and Germ Cell Research in Kennett Square.
Schöler and his colleagues got around the problem by linking a mouse gene called Oct4 to a fluorescent green marker from jellyfish. "We knew wherever that green color was showing up, that would be an indication for the germ cell," Schöler explains. Germ cells are sperm and egg cells.
After that, things were easy. "The astonishing thing [is] we didn't need any cocktail of growth factors and so on," Schöler says. "The only trick was to take the embryonic stem cells of the fetus, which are expressing all these growth factors, put them in high density on a plate and then they would turn on this green color." The green color was not necessary to the biological process, but let the scientists visualize what was happening at each stage of the game.
The eggs, or oocytes, also underwent meiosis (cell division) and developed into embryos, even though they weren't fertilized.
Being able to grow these cells outside the body of an organism will precipitate whole new lines of research. "Now we can start right from the beginning and go all the way through to try to understand the process of germ-cell formation," Schöler says. "It's much easier to study in a dish."
The breakthrough could impact a variety of fields, including fertility research. "We can use embryonic stem cells to generate oocytes and then see if there's a genetic reason for a person being infertile," Schöler explains. "It also means you can study what is going wrong."
Chromosomes from the oocytes can be removed and replaced by a new set of chromosomes in an example of nuclear transfer that could have implications for cloning.
The new procedure may also provide a way to produce embryonic stem cells so as to steer clear of the ethical concerns articulated by some politicians.
"You're basically creating various eggs for using, to make things," Sanberg says. "You could help them develop a lot of starting material to develop future embryonic cell lines. It would be really interesting to see this translated up to human stem cells. That's important."
Although mouse cells will allow much research to be done, Schöler hopes that one day the feat will be repeated in primates and other species. "If you would indeed like to develop therapies or at least explore the potential to develop therapies, I think you would rather include human stem cells," he says. "The process in mice is so simple I don't see a reason it wouldn't work with primate embryonic stem cells. It's not like we are developing a cocktail that is so sophisticated."
"I'm not going to say this is going to lead to therapeutic things at this stage, but it has potential. That is true," he says.
More information
The National
Institutes of Health has a basic primer on stem cells. Check out the University of Cincinnati for more on meiosis.
